Once several repositories carry Jenkinsfiles, the same checks, tagging rules and notification code turn up in each, and every copy needs the same fix. A shared library is a Git 1,932 repository of Groovy code that pipelines load by name, so the logic is written, reviewed, versioned and tested once. BookNest's library lives in its own public repository, github.com/binarybehemoth/booknest-jenkins-lib (https://github.com/binarybehemoth/booknest-jenkins-lib), and the multibranch job from Jenkinsfiles in Source Control now loads it.